If you’re thinking about buying a 3D printer, you might be surprised to find there are two distinct types of 3D printers: Fused Deposition Modeling (FDM) and resin. While both use plastic to create 3D prints, which you should get depends on several factors, from what and where you’ll print, to how much after-print fussing you are willing to do. Let’s take a closer look.
Additive Manufacturing---The Layer Cake of 3D Printing
FDM Printers---Creating an Object from a Roll of Plastic
SLA Resin Printers---Printing with Invisible Light
Making Your Decision
Additive Manufacturing—The Layer Cake of 3D Printing
Most 3D printing, especially at the hobbyist or prototype level, is created by a process called additive manufacturing. While it sounds complex, it’s actually just the technical term for creating an object by printing very thin layers, one on top of the other, to build up the desired print. This is true regardless of whether the process used is FDM (Fused Deposition Manufacturing), sometimes called FFF (Fused Filament Fabrication) printing, or by stereolithography, using a liquid plastic resin that hardens on exposure to ultraviolet light of a certain frequency. If you think of a cake made up of layers rather than just a hunk of cake, you’ve got the idea.
FDM Printers—Creating an Object from a Roll of Plastic
FDM 3D printing is currently the most popular form of low-to-moderately-priced 3D printing, though that’s changing as reasonably priced resin printers are flooding the market. FDM printing uses a roll of thin thread-like plastic that’s either 1.75mm or 3mm in diameter, with 1.75mm being the most popular. The thermoplastic filament is supplied on a plastic spool. The most popular size spool contains 1KG by weight of filament. Pretty much no vendor actually tells you how long the filament is, only what it weighs. That’s fine because most slicer software, which converts the 3D object model into Gcode that tells the printer where and how to print each layer, will often tell you how much filament in meters or feet the object will require.
Filaments for FDM 3D printers are available in a variety of different materials, each more suitable for printing different types of objects. The most popular and easiest to use from the viewpoint of specifying factors such as extruder temperature and other settings is PLA (Polylactic Acid), which is biodegradable, odorless, and does not require a heated build platform to adhere to. It’s also generally a bit less expensive than other filament materials.
ABS (Acrylonitrile Butadiene Styrene) is another popular filament and is usually a stronger and more durable material than PLA. It’s also a bit fussier about print parameters than PLA, needing a higher extruder temperature and a heated build plate for best results and to prevent warping. Other materials such as PETG (Polyethylene Terephthalate). TPU (Thermoplastic Polyurethane), Nylon, and other materials like filament that contains fillers such as metal or wood fibers, are also plentiful and allow you to print objects that look like metal, wood, or even carbon fiber.
The actual print process of filament printing can be thought of as a glue gun that moves in three dimensions. An extruder module unspools the plastic filament and drives it into the hot end (which is sometimes incorporated in the extruder), where it is melted and forced out of a metal nozzle. The hot end is moved in three dimensions–along the X-axis (side to side), the Y-Axis (front and back), and the Z-axis (up and down). With some printers, it’s the hot end that moves, and in some, the build platform moves in the X and Y axis, and the hot end moves in the Z-axis. The net result, in any case, is that a thin line of melted filament is laid down, first on the build platform for the first layer, then on top of each previous layer, building up the printed object layer-by-layer until the object is finished.
Things to consider with an FDM printer include what kinds of filament it can use, print bed size, and whether the print bed can be heated. A heated print bed is important if you want to use the widest variety of filament types. With many filament types, such as ABS, an unheated print bed may result in the inability of the object you are printing to stick to the print bed or cause the base of the printed object to warp as the plastic cools. And keep in mind that some plastics give off objectionable fumes when melted, so using them may require placing the printer where any fumes produced won’t be bothersome.
Another consideration is the software that comes with the printer. The application that comes with every printer, whether FDM or SLA, is called a slicer. The slicer converts the model’s image into instructions that control the printer and print quality. The language that 3D printers use is called Gcode.
Some printer vendors, such as XYZprinting, use their own slicer software. Other use the CURA software developed and maintained by printer vendor Ultimaker. CURA is released as open-source software, with individual printer vendors adding the printer profiles, which set some of the print parameters, to the list of supported printers. Some other popular slicers are KISSlicer, PrusaSlicer, Repetier, and Slic3r. If you think you might eventually purchase several FDM printers from different vendors, it might make sense for you to use a universal slicer like CURA, which supports hundreds of different printer models from numerous vendors.
SLA Resin Printers—Printing with Invisible Light
A second 3D print technology is stereolithography, often abbreviated as SLA. Stereolithography was the first 3D print technology and was invented in 1986. SLA 3D printers use a form of liquid resin that hardens on exposure to ultraviolet light by a process called photopolymerization. In most hobbyist SLA printers, this light source is a UV LED shining through an LCD panel that allows some light to pass and blocks others. When the pass-through UV light hits the resin layer, it hardens the plastic on a build platform that moves vertically and exposes more liquid resin to create the object layer by layer.
There is an enormous number of resins available, and many are for specialized printing of specific kinds of resin 3D prints. These include hard plastic, flexible plastic, resin for jewelry making and lost wax casting, and resins used in dental labs. The standard resin is available from a dozen or more vendors and is sold by the liter (or half-liter).
Resin printers are messy and toxic. The resin can get on your hands or in your eyes, and nitrile gloves and eye protection are suggested. Almost all of the resins used in 3D printing give off fumes and require use in a well-ventilated area. Resin printing has some serious shortfalls for the beginning user, including specialized slicers, small build plates; and the need for post processing, including an isopropyl alcohol wash and UV curing of the outside of the object (though leaving it in the sun for several hours accomplishes this). If you choose resin printing, a worthwhile accessory is a wash and cure station, which can cost $100 or more. Many resin 3D printer manufacturers also create matching cure stations that are compatible with each other. Resin printing used to be a lot more expensive than FDM printing, but the prices on resin printers have fallen to be competitive.
Making Your Decision
For many potential purchasers, an FDM filament printer will be the way to go for your first 3D printer. Resin printing is messy, creates fumes, and requires a considerable amount of after-printing finishing, including some sort of UV print box to cure the outermost layer of resin or leaving the object out in the sun to harden the surface layer. Excess resin also has to be disposed of carefully; you can’t just rinse it in the sink or flush it down the toilet. FDM Filament printers are simply less expensive and easier to use (at least to start).
Still, for all the messiness, fussiness, and fumes, resin-printed objects tend to be more detailed and show less layering. Resin printers are very popular for printing miniatures. The slicer included with resin printers differs somewhat from those shipped or available for an FDM printer. They still accomplish the same function, converting models into code that the printer can execute. Still, as a resin printer functions differently from an FDM unit, the code is also different. Many resin printers come with a slicer called Chitubox, and the Prusa slicer will also work with SAL printers.
Regardless of which technology you choose, there are thousands of 3D object files online and available free for downloading. A good place to start is on Makerbot’s Thingiverse.com. Starting your 3D printing endeavors with one of these is a terrific way to build experience.